Irish Calculators
Business

Cost of Debt and Optional Tax Shield Calculator

Estimate the pre-tax cost of debt and, if applicable, its after-tax equivalent. The tax rate and full deductibility are entered assumptions rather than an automatic assessment of Irish tax relief.

Runs privately in your browserMethod reviewed

Your numbers

%
Your figures stay on this device.

How the calculation works

Measure the annual financing cost of an existing debt balance. This calculation relates interest and annualised charges to average debt, with an optional tax adjustment when the full assumed deduction is applicable.

Pre-tax cost = (annual interest + annualised financing fees) / average interest-bearing debt. With a full usable tax shield, after-tax cost = pre-tax cost × (1 − tax rate).

  1. Build the annual cost

    Add annual interest and annualised fees. Keep the coverage period consistent so this numerator represents the cost of carrying the debt in the denominator.

  2. Relate cost to debt

    Divide that total by positive average debt, then multiply by 100. This produces a cost percentage rather than a quoted coupon alone.

  3. Apply the optional adjustment

    When enabled, multiply the pre-tax cost by one minus the supplied tax rate. This simplified adjustment assumes the deduction can be used in full.

Worked example: No shield

Sample inputs demonstrate the method. They are not a forecast or product offer.

Annual interest of €8,000 plus €2,000 of annualised fees gives €10,000. Dividing by average debt of €100,000 produces 10%. With the tax adjustment switched off, both displayed cost measures remain 10%.

Annual interest expense
8000
Annualised financing fees
2000
Average interest-bearing debt
100000
Tax-shield assumption
No tax shield assumed

Expected result

Pre-tax cost of debt
10%
Tax-adjusted cost of debt
10%
Worked example: Full shield

Sample inputs demonstrate the method. They are not a forecast or product offer.

Annual interest expense
10000
Annualised financing fees
0
Average interest-bearing debt
200000
Tax-shield assumption
Full entered cost is deductible
Applicable marginal tax rate (%)
20

Expected result

Pre-tax cost of debt
5%
Tax-adjusted cost of debt
4%

Understanding your result

Compare periods only after checking that both use the same debt and fee definitions. A lower percentage may reflect different borrowing composition as well as cheaper funding.

This ratio is not a contractual APR or an effective yield calculated from dated payments. It does not price a new loan or determine a tax saving.

Questions you might have

Why use average debt rather than year-end debt?

The expense was earned over time. A closing balance can distort the rate when borrowing changed substantially during the year.

Choosing the right inputs

Average interest-bearing debt
Use average interest-bearing debt supporting the annual charges. A closing balance can distort the ratio when borrowing changed substantially during the year.
Annualised financing fees
Enter the portion of financing fees allocated to this year. The calculator does not spread an upfront arrangement charge across several years automatically.
Tax-shield assumption
Choose the adjustment only when the costs qualify for the full assumed tax shield. The form does not establish deductibility.

Common mistakes to avoid

  • Do not put total liabilities in the denominator when the interest relates only to interest-bearing borrowing.
  • Do not count the full upfront fee and an annual allocation of that same fee together.

Assumptions to check

  • Use amounts in one currency and one reporting period. Results are labelled EUR; the arithmetic also works for another consistent currency.
  • The tax rate is an assumption supplied by the user, not an Irish entitlement determined here.

Sources and method

Read our calculation and testing approach.